Solvent fractionation of waxcontaining mixtures



Jan. 20, 1953 w, cLARKE 2,626,231

SOLVENT FRACTIONATION OF WAX-CONTAINING MIXTURES Original Filed Sept. 16, 1947 EXT N. SOLVENT 1 ADDITIVE.

2L ADDITIVE ATTEST INVENTOR. Edy'ar WCldr/ c (1034} BY M K/Ju/ Patented Jan. 20, 1953 UNITED STATES PATENT OFFICE SOLVENT FRACTIONATION OF WAX- CONTAINING MIXTURES Edgar W. Clarke, Laurel Springs, N. J assignor to The Atlantic Refining Company, Philadelphia, Pa., a corporation of Pennsylvania Original application September 16, 1947, Serial Divided and this application November 5, 1949, Serial No. 125,731

3 Claims. 1

The present invention relates to the treatment of oily waxes, and more particularly to the separation of wax-containing mixtures into fractions of higher and lower melting point, using a solvent comprising nitrobenzene, and additives compris- .ing furfural and paraflinic naphtha or kerosine.

' fractions of different melting point. The process of the present invention may be applied in the refining, purification, or separation of wax stocks such as petroleum slack wax, crude microcrystalline wax, paraffin waxes, petrolatum wax, montan wax, ceresin, ozokerite, waxes from the destructive or non-destructive hydrogenation of mineral oil, synthetic hydrocarbon oil, shale oil,

coal, and waxes produced synthetically by the catalytic reaction of hydrocarbons, or waxes derived from the modified Fischer-Tropsch reaction of carbon monoxide and hydrogen. The process of this invention is especially applicable I in the separation of wax mixtures containing color bodies and oil into a higher melting wax fraction of light color and low oil content, and

- a lower melting wax fraction of darker color and containing most of the oil originally present in the wax mixture.

In accordance with this invention, a wax-containing mixture is separated into fractions of higher and lower melting point by countercurrently contacting the wax-containing mixture in an extraction zone with an extraction solvent and a solvent additive or additives at a temperature such that two liquid phases are formed, one comprising the higher melting wax fraction with minor amounts of solvent and additive, and the other comprising the lower melting wax fraction with major amounts of solvent and additive, separating the liquid phases from one another, and removing the solvent and additive from each.

The extraction solvent and additives employed may have a density greater than that of the wax. However, when the additive or additives are partially immiscible with the extraction solvent and are less dense than such solvent or the wax, the additive or additives will flow countercurrent to the extraction solvent and will appear a with that liquid phase comprising the higher meltin wax fraction. The succes or the processdepends upon the control of the temperature throughout the extraction zone and upon the regulation of the proportions of solvent and additive used, and the points of introduction of the wax-containing mixture, the solvent, and the additive into the extraction zone.

The extraction solvent may be defined as an agent which, when intimately mixed with a waxcontaining mixture, forms two liquid phases or layers, one comprising a rafiinate phase containing mostly wax of higher melting point than the untreated wax and a portion of the solvent, and the other comprising an extract phase containing mostly solvent, and wax of lower melting point than the untreated Wax, as well as a majo portion of the color bodies and oil originally present in the untreated wax.

The solvent additive may be defined as an agent used in conjunction with the extraction solvent for the purpose of modifying the characteristics of the extraction solvent. The additive may lower the temperature at which solid wax precipitates out of the extraction solvent, or it may raise the miscibility temperature of the extraction solvent with the wax. However, the additive chosen for a particular extraction solvent must not excessively lower the selectivity of the extraction solvent at the temperature of extraction.

The extraction solvent may be employed in amounts ranging from 1 to 5 volumes of solvent per volume of untreated wax stock, while the additive or additives may be used in amounts ranging from 0.05 to 1 volume per volume of untreated wax.

The extraction solvent which may be employed in accordance with the present invention comprises nitrobenzene containing a small amount, for example 5% to 10%, of furfural.

The solvent additive or additives, which are usually employed in amounts constitutin not more than 50% by volume of the extraction solvent, include furfural and paramnic hydrocarbone of from 8 to 18 carbon atoms, preferably Referring to the drawing, a waxecontaining mixture is continuously introduced, in liquid condition, into the extraction tower lythIOtlg-hWfiJVG- controlled pipe 2 at a rate-of l-volumesper hour. An extraction solvent comprising nitrobenzene containing ;,of;;furfural is continu-;

ously introduced from vessel.3 bymeans'ofrvalvecontrolled pipe 4 and manifold 5 into theupper section of the tower below the rafiinateoutlet at a rate of 200 volumes per hour. The first additive comprising furfural is continuously introduced from 'vessel"'6' through-valve-controlled-pipe' 'I ",intothe extraction tower-lbelow thewax inlet at a rate of'40'volumes' per-hour. Thesecond additive comprising paraihnic-kerosene boiling be- 'tween'400 F. and'600 F; is continuously introduced from storage vessel tl by valve-controlled pipe 'B' intothe extractiontower l between the point of'intro'duction ofthe first additive and the outlet of-the-extract' phase, at arateof 50 volumes per hour. An intimate countercurrent contacting of the wax stock, the extraction solvent,

and-theadditives is efiected in tower I, a temperaturegradient beingmaintainedin the tower by means of coils through which a heating or cooling medium is circulated as requiredythe temperature adjacent the-top of the tower being higher than that adjacent'the'bottom of the towerythe contents of "the tower being entirely in'the'liquid phase. The wax stock; being subjected to the action ofthe solvent andadditives,

" '-ing--wax--- and dissolved solventand additives is 'passedfrom thetop of *tower' l-throughvalve- -cont'rol-led" pipe I 3 into -a-vacuum evaporatoror still 14 wherein the solvent and additives are removed from-the higher melting wax byvaporizat-ion;'the solvent and additive vapors being de- "livered through pipe 15' to condenser l5, condensed, and the condensate is passed-by pipe 11 to separator 18 provided with a temperature control coil' l9. "The higher -melting wax is'drawn from the bottom of evaporator 14 and "delivered "by valve-controlled pipe 20 into storage'vessel 2 I "Such-wax fraction "was white in' color, and'had a -substantia-lly higher melting'point and a lower oil content than the waxy stock originally --'charged.

The extract phase comprising the lower melting wax fraction, color bodies, oil,-- and the major portion of the extraction solvent and the first additive and a minor proportion ofthe second -additive,-is withdrawn fromthe lower section of -tower'l beneath the level of the dotted line 22 "representing the extract phase relatively free of -entrained, "higher melting wax. The extract phase is delivered by valve-controlled pipe 23 into a vacuum evaporator or still 24 wherein the solvent and additive is vaporized from the lower melting wax, the latter being drawn from the bottom of the evaporator; and wpassed by valve- -controlled pipe 25 to storage vessel 26. "The lower melting wax was brown in color and had a lower melting point and a higher oil content than the original Waxystock.

r-The-solvent and additive vapors are passed from the top of evaporator 24 through pipe 21,

=condensed in condenser 23, and the condensate is delivered by pipe 29 to separator I8. In separator I 8, theparafiinic kerosene (second additive) forms an upperlayer above the immiscible mixxture comprising nitrobenzene (solvent) and furfural (firstpadditive). The parafiinic kerosene is separate-d and returned by pipe 30 to storage vessel 9, while the nitrobenzene and furfural are passed by pipe 3! to fractionating tower 32 provided with reboiler or heating coil-33. ""In tower 32 the furfural is fractionally distilled from the nitrobenzene, and the latter is drawn as aliquid bottoms and returned by pipe-34 to .storagevessel 3. The furfuralis taken from the top. of :the tower, as vapor, and passediby -pipe ;35. to ,condenser 36, condensed therein, and-returned by pipe 31 to storage vessel 6. .A portion ofthe condensate may be recycled byvalve-controlledpipe 33 to the top of tower: 32 as reflux.

The nitrobenzene returned to :vessel :3 .zmay contain small amounts of furfural andv additional furfural may be incorporated in the nitrobenzene to bring the furfuralcontent up to .l0.%; in--the solvent contained in vessels. Thismay 'be. accomplished by introducing-furfural from :vessel 6 by means-of valve-controlled pipe ii Depending upon the temperature of operation, the first additive may be introducedsomewhat above the point of introduction of the liquefied wax stock, for example, byVmeans-of valve-controlled pipe [6 rather than through .valveecontrolled pipe 1, .or the first additivemay be introduced byboth pipes'l. and 19. In ,general, :the rafiinate wax phase withdrawn from the extraction tower will containfrom 5% to,25% ofsolvent and-additive, while the extract ,waxphase willpcontainfrom,55% to ;,of:so1v ent and additive.

'While, in the extraction system aboe d e- .s ib s a pec fi c mb nation organ extrac ion olvent; a d add t v reusedritis obviousthat various other combinations maybee 1p yed, de-

p din upon th n tur .ofi-th :wa .'stoc ;-t0 be treated, h ct on:t m er ture ,.a iheextent to whioh the wax stocl is' to besenarated naphtha or kerosene, would be introduced into the first stage extractor, from which the extract phase is withdrawn, while the raffinatephase would be removed from the fourth stage extractor. The temperature would increase progressively from thefirst stage to the fourthstage, using the waxy stock, solvent, andadditives de- -scribed .helieinabove. ,It is ,to .be -understood,;of

course, that the quantities and composition of the solvent and of the additives may be varied within certain limits.

When the second additive comprises hydrocarbons such as C8 to C18 paraffin hydrocarbons, paraffinic naphtha, or paraffinic kerosene, these additives would leave the extrac- Extraction solvent 1st Additive 2d Additive Paraifinlc naphtha or kerosene, 0.55:0. vo

Nitrobenzene+% Furfural 0.4d=0.1 vol.

furfural 2=l=0.2 vol.

The present invention is further illustrated by the following example, which, however, is not to be construed as limiting the scope thereof.

(1) A slack wax having a melting point of 113 F. and an oil content of 24.2% by weight was extracted in a system similar to that shown in the accompanying drawing, the extraction solvent comprising 2 volumes of nitrobenzene containing 10% of furfural, the first additive comprising 0.4 volume of furfural, and the second additive comprising 0.5 volume of parafiinic kerosene. The temperature in the extraction tower was held constant at 90 F. After countercurrent contacting and removal of the raffinate phase from the top of the tower, and the extract phase from the bottom of the tower, the solvent and additives were recovered from the wax fractions by vacuum evaporation and fractionation. The results are given in the following table.

Where the extraction operation is conducted in a tower, it has been found that a tower having a height of about 40 feet and a diameter of 6 feet is satisfactory. The tower is provided with suitable packing to within about 4 feet of the top and bottom thereof, such spaces functioning as quiescent zones in which entrained materials are permitted to separate from the ramnate and extract phases, respectively. In such a tower, the wax stock is charged at a point about 13 feet from the bottom thereof, or approximately /3 the distance from the bottom of the tower. The extraction solvent is charged just above the upper level of the packing, for example, 3 to 4 feet from the top of the tower. The first additive may be introduced adjacent the point of introduction of the wax stock, for example, 2 feet above or below the wax inlet. The second additive is introduced approximately 2 feet below the point of introduction of the first additive. These values'may be altered somewhat, depending upon the tower design, the solvent and additives used. and the temperatures maintained at various levels in the tower. The raffinate phase is withdrawn from the top of the tower, and the extract phase from the bottom thereof, the extraction solvent being more dense than the wax stock.

I claim:

1. The method of separating a wax-containing mixture into fractions of higher and lower melting point, which comprises counter-currently contacting said wax-containing mixture in an extraction zone with an extraction solvent and solvent additives at a temperature such that two immiscible liquid phases are formed, one comprising the higher melting wax fraction containing solvent and additives, and the other comprising solvent and additives and the lower melting wax fraction, separating the phases from one another, and removing the solvent and additives from each, the solvent being introduced into the extraction zone near the point of withdrawal of the higher melting wax fraction, the first additive being introduced adjacent the point of introduction of the wax-containing mixture, and the second additive being introduced between the point of introduction of the first additive and the point of withdrawal of the lower melting wax fraction, the solvent comprising 1.8 to 2.2 volumes of nitro benzene containing a small amount of furfural per volume of wax-containing mixture, the first additive comprising 0.3 to 0.5 volume of furfural per volume of wax-containing mixture, and the second additive comprising 0.45 to 0.55 volume of a paraffinic hydrocarbon containing from 8 to 18 carbon atoms per volume of wax-containing mixture.

2. The method of separting a wax-containing mixture into fractions of higher and lower melting point, which comprises counter-currently contacting said wax-containing mixture in an extraction zone with an extraction solvent and solvent additives at a temperature such that two immiscible liquid phases are formed, one comprising the higher melting wax fraction with minor amounts of solvent and additives, and the other comprising the lower melting wax fraction with major amounts of solvent and additives, separating the phases from one another, and removin the solvent and additives from each, the solvent being introduced into the extraction zone near the point of withdrawal of the higher melting wax fraction, the first additive being introduced between the point of introduction of the wax-containing mixture and the point of withdrawal of the lower melting wax fraction, and the second additive being introduced between the point of introduction of the first additive and the point of withdrawal of the lower melting wax fraction, the solvent comprising 1.8 to 2.2 volumes of nitrobenzene containing a small amount of furfural per volume of wax-containin mixture, the first additive comprising 0.3 to 0.5 volume of furfural per volum of wax-containing mixture, and the second additive comprising 0.45 to 0.55 volume of paramnic kerosene per volume of wax-containing mixture.

3. In a method of separating a wax-containing mixture into fractions of higher and lower melting point, wherein the wax-containing mixture is contacted in an extraction zone with an extraction solvent and solvent additives at a temperature above the melting point but below the temperature of complete miscibility of the mixture, the steps which comprise introducing 1 volume of liquefied wax-containing mixture into the extraction :zone a at a point intermediate -=the p i .of with'drawal of the highenand lower melting waxes. including the solvent and additive, introducing 1.8 tor2.2 volumes of extractionsolvent comprising nitrobenzene containing 10% of furfural at a point adjacent the point of withdrawal of theihigher melting .Wax fraction including solvent and additive, but intermediate said point of withdrawal and thezpoint of introduction of the liquefied wax-containing mixture, and introducing 0.3 to 0.5 volume of an additive comprising furfural intermediate the point of introduction of the liquefied wax-containing mixture and-the point of withdrawal of the lower melting wax fraction including solvent and additive, introducing;0.4.5 to 0.55 volumes ofan additive comprising parafiinic kerosene at .a point intermediate the pointof introduction of the first additive and the point of withdrawal of the lower meltingwax fraction including solvent andadditive, efiecting countercurrent contact between the liquefied wax-containing mixture and the solvent and 8 additives at Y temperature suohn-that. two inimiscible liquid phases arezformed, onephaseoornprising-the higher melting, Wax 'fraction containing solvent and additives, and the other liquid phase comprising the lower melting waxfraction andtsolvent and additives, thetemperature in the extraction zone increasing in the direction of .flow 0f the higher melting wax fraction, separately withdrawing the respective liquid phases from the extraction zone, and removing thesolvent and additives from each.

EDGAR W-. CLARKE.

REFERENCES CITED The following referencesare of record in-the file of this patent:

UNITED STATES PATENTS Number Name Date 20 2,017,432 Bahlke Oct. 15, 1935 2,138,833 Brown et a1. 'Dec. 6, I938 2,160,930 Whiteley et al. June 6, 1939 

1. THE METHOD OF SEPARATING A WAX-CONTAINING MIXTURE INTO FRACTIONS OF HIGHER AND LOWER MELTING POINT, WHICH COMPRISES COUNTER-CURRENTLY CONTACTING SAID WAX-CONTAINING MIXTURE IN AN EXTRACTION ZONE WITH AN EXTRACTION SOLVENT AND SOLVENT ADDITIVES AT A TEMPERATURE SUCH THAT TWO IMMISCIBLE LIQUID PHASES ARE FORMED, ON COMPRISING THE HIGHER MELTING WAX FRACTION CONTAINING SOLVENT AND ADDITIVES, AND THE OTHER COMPRISING SOLVENT AND ADDITIVES AND THE LOWER MELTING WAX FRACTION, SEPARATING THE PHASES FROM ONE ANOTHER, AND REMOVING THE SOLVENT AND ADDITIVES FROM EACH, THE SOLVENT BEING INTRODUCED INTO THE EXTRACTION ZONE NEAR THE POINT OF WITHDRAWAL OF THE HIGHER MELTING WAX FRACTION, THE FIRST ADDITIVE BEING INTRODUCED ADJACENT THE POINT OF INTRODUCTION OF THE WAX-CONTAINING MIXTURE, AND THE SECOND ADDITIVE BEING INTRODUCED BETWEEN THE POINT OF INTRODUCTION OF THE FIRST ADDITIVE AND THE POINT OF WITHDRAWAL OF THE LOWER MELTING WAX FRACTION, THE SOLVENT COMPRISING 1.8 TO 2.2 VOLUMES OF NITROBENZENE CONTAINING A SMALL AMOUNT OF FURFURAL 